The present invention relates to a surveying instrument, by which it is possible to perform a measurement with high accuracy and quickly by compensating a deviation of an optical axis of a measuring light when the deviation occurs on the optical axis of the measuring light due to vibration.
A surveying instrument is used to perform a distance measurement and a measurement of a horizontal angle and a vertical angle by directing the optical axis of the measuring light of a distance measuring light optical system toward an object to be measured. A surveying instrument with tracking function has a rotator, and the rotator is rotated to follow the movement of the object to be measured. The optical axis of the measuring light is directed toward the object to be measured, and the measurement can be performed on the object to be measured.
When the surveying instrument is installed, leveling is carried out on the surveying instrument so that a vertical axis of the surveying instrument concurs with a gravitational direction. The leveling operation is carried out by using a tilt sensor provided on the surveying instrument. The surveying operation is performed with the surveying instrument under leveled condition.
In the meantime, even when the surveying instrument is leveled accurately in standard condition, a posture of the surveying instrument may be deviated, although slightly, when the rotator driven or stopped. Also, a slight angular error may occur during the driving due to an inertial force of a driving unit. In case the measurement is performed dynamically, the error may exert influence on a measured value. Or, the deviation may occur in the leveling condition of the surveying instrument due to causes subsequently occurred, such as the vibration from outside or the like. Under the condition where the deviation has occurred in the leveling condition, an error may be included in the measured value, and an accurate measurement may not be carried out.
Therefore, in the past, in case the deviation occurs in the leveling condition of the surveying instrument—for instance, in case the device is tilted, it has been practiced to detect the tilting and to compensate a measurement result based on a result of the detection.
In the past, to detect the tilting of the surveying instrument, the tilting has been detected with high accuracy by using an air bubble tube type tilt sensor or a tilt sensor to detect the tilting of liquid surface, which are provided on the surveying instrument for the purpose of leveling,
The tilt sensor can detect the tilting of the surveying instrument with high accuracy, but it requires longer time for detecting. Further, because a tracking operation is carried out or the like, immediately after the rotator is driven and stopped, a signal from the tilt sensor is not stable due to the vibration caused at the time of stopping. Thus, it is not possible to accurately detect the tilting. Accordingly, it is necessary to wait for some time until the vibration ceases to exist and the tilt sensor can be stabilized. Further, the measurement error may occur during operation.
Also, the tilt sensor does not exhibit high responsiveness and does not response accurately to the vibration from outside—for instance, to the vibration caused by the passing of an automobile on a road near the point where the surveying instrument is installed. Therefore, it has been practiced to perform averaged processing in view of time to the detection signal from the tilt sensor. The tilting in average has been determined, and the measured value has been compensated based on the tilting obtained by the averaged processing.
For this reason, variations in the measurement data are increased because of the vibration.
In some type of the surveying instrument, a pulsed distance measuring light is projected at high speed by rotary irradiation via the rotator and the position of the object to be measured is measured. In this type of surveying instrument, the high inertial force occurs due to stopping or driving of a motor and the rotator, and the posture of the surveying instrument is changing at every moment. In this respect, the tilt sensor as described above exhibits low responsiveness, and the change of posture cannot be detected accurately. Thus, compensation cannot be made with high accuracy.
As the surveying instrument to detect the tilting and to compensate the tilting of the instrument by using the tilt sensor is disclosed in JP-A-06-347271, JP-A-08-43098 and JP-A-2006-78416. The surveying instrument to measure the position of the object to be measured by projecting a laser beam for a position measurement by rotary irradiation is disclosed in JP-A-2004-212058 and JP-A-2007-170902.